Many tens of thousands of tonnes of high purity nitrogen are produced each year worldwide. This nitrogen is produced by the well-known process of fractionally distilling air at cryogenic temperatures. The nitrogen produced typically has a purity of at least 99.9% which makes it suitable for use in a wide range of industrial processes. The main impurity in the high purity nitrogen is argon and typically there might be in the order of 150 volumes per million of argon present. In addition, the nitrogen will also contain a few volumes per million of chemically reactive gases comprising oxygen, hydrogen and carbon monoxide. The nitrogen may also contain some tens of volumes per million of neon and a few volumes per million of helium. The hydrogen, oxygen and carbon monoxide impurities although at an extremely low level are still nonetheless undesirable when it is required to use the nitrogen in the fabrication of micro-electronic products. Accordingly, there is a demand for nitrogen of an even higher purity than that normally provided.
One way of meeting this demand has been to subject the nitrogen to a process of catalytic combustion to remove traces of the reactive gases. However, in some instances, this process is not suitable because the gas becomes contaminated with particles generated from the catalyst granules. Alternative adsorptive purification methods are known but these too involve a risk of contamination by particles from the adsorbent granules.
There is thus a need for new methods of producing nitrogen to a higher standard of purity than has hitherto been achieved by conventional cryogenic methods.